Polyaxial bone fixation element

ABSTRACT

A fastener device includes an anchor body that defines a through hole. The anchor body further includes an inner surface that defines a least a portion of the through hole. The fastener includes a head, a threaded shaft that extends out with respect to the head in a distal direction, and a neck between the head and threaded shaft. The head includes an outer surface configured to articulate along the inner surface when the fastener head is inserted in the through hole. At least a portion of the outer surface is convex and defines a portion of a sphere that defines a first diameter. The neck defines a second diameter and the fastener defines a ratio of the first diameter to the second diameter in a range between about 2 to 1 and about 3 to 1.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 15/441,326filed Feb. 24, 2017, which claims the benefit of U.S. ProvisionalApplication No. 62/300,456, filed Feb. 26, 2016, the contents of whichare hereby incorporated by reference as if set forth in their entiretyherein.

TECHNICAL FIELD

The present application relates generally to medical devices. Morespecifically, the present application is related to devices, kits, andmethods for treatment of a spine.

BACKGROUND

Various spinal disorders may be surgically corrected to stabilize apatient's spinal column. Spinal disorders may include curvatures orother defects that are correctable with a spinal fusion procedure. Onemethod of spinal fusion involves one or more elongated members,typically spinal rods, longitudinally placed on the posterior spine.When a pair of elongated members is used in the spinal fusion procedure,the elongated members may be placed on either side of spinous processesof the vertebral column, for example.

Each elongated member may be attached to one or more of the vertebrae ofthe spine by way of fastener devices. The fastener devices each mayinclude an anchor body defining a rod-receiving channel configured toreceive a portion of the elongated member therein, and a locking capconfigured to clamp and secure the position of the elongated memberwithin the rod-receiving channel. The fastener devices each may furtherinclude a fastener configured to secure the anchor body to a vertebra.

To facilitate insertion of the elongated members into the rod-receivingchannels and to provide additional flexibility in the positioning of theelongated members and the fastener devices, fastener devices have beendeveloped wherein the anchor body is pivotable with respect to thefastener. These fastener devices may be referred to as polyaxialfastener devices.

It is desirable to develop a fastener device that is simple for asurgeon to use, that provides for polyaxial rotation and is able tosecurely mount the elongated member to a patient's spine.

SUMMARY

In accordance with an aspect of the disclosure, the present applicationdiscloses a fastener device comprising an anchor body and a fastener.The anchor body including an anchor body housing, the anchor bodydefining a through hole that extends through the anchor body housing,the anchor body further including an upper end, a lower end, and aninner surface, and the inner surface defining a least a portion of thethrough hole. The fastener including a head, a threaded shaft thatextends out with respect to the head in a distal direction, and a neckthat extends between the head and the threaded shaft. The head includingan outer surface configured to articulate along the inner surface whenthe fastener head is inserted in the through hole, at least a portion ofthe outer surface being convex and defining a portion of a sphere, thesphere defining a first outer diameter, and the fastener including aconcave surface that extends along both the head and the neck, the neckdefining a second outer diameter measured: 1) in a directionperpendicular to the distal direction, and 2) at a location spaced inthe distal direction of an entirety of the concave surface, wherein thescrew defines a ratio of the first outer diameter to the second outerdiameter in a range between about 2 to 1 and about 3 to 1.

In accordance with an aspect of the disclosure, the present applicationdiscloses a fastener device comprising an anchor body and a fastener.The anchor body including an anchor body housing, the anchor bodydefining a through hole that extends through the anchor body housing,the anchor body further including an upper end, a lower end, and aninner surface that defines a least a portion of the through hole, and atleast a portion of the inner surface defining a portion of a firstsphere. The fastener including a head, a threaded shaft that extends outwith respect to the head in a distal direction, and a neck that extendsbetween the head and the threaded shaft. The head including an outersurface, at least a portion of the outer surface defining a portion of asecond sphere, and the head further including a concave surface of thefastener that extends along both the head and the neck. The fastenerdevice defines a configuration in which both: 1) the portion of theouter surface rides along the portion of the inner surface, and 2) theanchor body abuts the neck at a location that is spaced in the distaldirection from an entirety of the concave surface such that movement ofthe fastener relative to the anchor body in at least one direction isblocked.

In accordance with an aspect of the disclosure, the present applicationdiscloses a fastener device comprising an anchor body and a fastener.The anchor body including an anchor body housing, the anchor bodydefining a through hole that extends through the anchor body housing,the anchor body further including an upper end, a lower end, and aninner surface, and the inner surface defining at least a portion of thethrough hole. The fastener including a head, a threaded shaft thatextends out with respect to the head in a distal direction, and a neckthat extends between the head and the threaded shaft. The head includinga convex outer surface, a portion of the convex surface both defining aportion of a sphere and being configured to articulate along the innersurface when the fastener head is positioned in the through hole, andthe fastener including a concave surface that extends along both thehead and the neck. Wherein the fastener is configured such that alllines that: 1) lie entirely within a plane parallel to the distaldirection, and 2) are tangent to the portion of the convex outer surfaceare noncollinear with all lines that: 1) lie entirely within the plane,and 2) are tangent to the concave surface.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofillustrative embodiments of the application, will be better understoodwhen read in conjunction with the appended drawings. For the purposes ofillustrating the present disclosure, there is shown in the drawingsillustrative embodiments. It should be understood, however, that theapplication is not limited to the specific embodiments and methodsdisclosed, and reference is made to the claims for that purpose. In thedrawings:

FIG. 1 is an isometric view of a fastener device, according to an aspectof the disclosure;

FIG. 2 is an exploded isometric view of the fastener device illustratedin FIG. 1 ;

FIG. 3 is a top plan view of a fastener of the fastener deviceillustrated in FIG. 1 ;

FIG. 4 is a side elevation view of the fastener illustrated in FIG. 3 ;

FIG. 5 is a cross-sectional view of the fastener illustrated in FIG. 3 ,along line 5-5;

FIG. 6 is a top plan view of an anchor body of the fastener deviceillustrated in FIG. 1 ;

FIG. 7 is a cross-sectional view of the anchor body illustrated in FIG.6 , along line 7-7;

FIG. 8 is a cross-sectional view of the fastener device illustrated inFIG. 1 , along line 8-8, the fastener device in a first configuration;

FIG. 9 is a cross-sectional view of the fastener device illustrated inFIG. 1 , along line 8-8, the fastener device in a second configuration;

FIG. 10 is a cross-sectional view of the fastener device illustrated inFIG. 1 , along line 8-8, the fastener device in a third configuration;

FIG. 11 is a cross-sectional view of the fastener device illustrated inFIG. 1 , along line 8-8, the fastener device in the secondconfiguration;

FIG. 12 is an exploded isometric view of a fastener device according toan aspect of the disclosure, the fastener device including a biasingmember and an anchor body;

FIG. 13 is a top plan view of the biasing member illustrated in FIG. 12;

FIG. 14 is a cross-sectional view of the anchor body illustrated in FIG.12 , along line 14-14;

FIG. 15 is a cross-sectional view of the biasing member and the anchorbody illustrated in FIG. 12 , along line 14-14, the biasing member andthe anchor body in an assembled configuration;

FIG. 16 is a cross-sectional view of the fastener device illustrated inFIG. 12 , along line 14-14, the fastener device in a firstconfiguration; and

FIG. 17 is a cross-sectional view of the fastener device illustrated inFIG. 12 , along line 14-14, the fastener device in a secondconfiguration.

DETAILED DESCRIPTION

Certain terminology is used in the following description for convenienceonly and is not limiting. The words “lower” and “upper” designatedirections in the drawings to which reference is made. The words“proximally” and “distally” refer to directions toward and away from,respectively, the surgeon using the medical device. The words,“anterior”, “posterior”, “superior”, “inferior” and related words and/orphrases designate preferred positions and orientations in the human bodyto which reference is made and are not meant to be limiting. Theterminology includes the above-listed words, derivatives thereof andwords of similar import.

Aspects of the disclosure will now be described in detail with referenceto the drawings, wherein like reference numbers refer to like elementsthroughout, unless specified otherwise. Certain terminology is used inthe following description for convenience only and is not limiting. Theterm “plurality”, as used herein, means more than one. The terms “aportion” and “at least a portion” of a structure include the entirety ofthe structure. Certain features of the disclosure which are describedherein in the context of separate embodiments may also be provided incombination in a single embodiment. Conversely, various features of thedisclosure that are described in the context of a single embodiment mayalso be provided separately or in any subcombination.

Reference herein to a first structure articulating along or riding alonga second structure refers to the first structure directly contacting thesecond structure, and precludes an intermediate structure or surfacebetween the first structure and the second structure.

Referring to FIGS. 1 and 2 a medical device 10 is configured to securean elongated member to a portion of a patient's anatomy. As shown in theillustrated embodiment, the medical device 10 can include a fastenerdevice 12 configured to secure a spinal rod 14 to a patient's vertebra,for example a pedicle or lateral mass of the patient's vertebra. Thefastener device 12 may be referred to as a pedicle screw when thefastener device 12 is configured to secure the spinal rod 14 to thepedicle of the patient's vertebra. According to one aspect of thedisclosure, the fastener device 12 includes an anchor body 16 configuredto receive the spinal rod 14, and a fastener 18 configured to beinserted into the anchor body 16 and secured to the patient's vertebra.

The fastener device 12 may further include a saddle 20 and a cap 22. Asshown in the illustrated embodiment the saddle 20 is configured to abutboth the fastener 18 and the spinal rod 14, and the cap 22 is configuredto secure the spinal rod 14 relative to the fastener device 12, asdescribed in further detail below.

According to one aspect of the disclosure, the anchor body 16 includesan upper end 24, a lower end 26 spaced from the upper end 24 in alongitudinal direction L, and an anchor body housing 28 that extendsfrom the upper end 24 to the lower end 26. The anchor body 16 defines athrough hole 30 that extends through the anchor body housing 28. Thefastener 18 includes a head 32, a threaded shaft 34 that extends outwith respect to the head 32 in a distal direction D, and a neck 36 thatextends between the head 32 and the threaded shaft 34. The fastener 18is configured to be positioned into the anchor body 16 by moving thefastener 18 in the longitudinal direction L, until the threaded shaft 34passes through the lower end 26 and the head 32 is positioned within thethrough hole 30.

The fastener device 12 is configured such that when the head 32 ispositioned in the through hole 30 the fastener 18 is movable,polyaxially, with respect to the anchor body 16. When the head 32 ispositioned in the through hole 30, the saddle 20 can be moved in thelongitudinal direction L, until the saddle 20 contacts the head 32. Whenthe saddle 20 is contacting the head 32, the spinal rod 14 can then bemoved in the longitudinal direction L until the spinal rod 14 contactsthe saddle 20. When the spinal rod 14 is contacting the saddle 20, thecap 22 can be moved in the longitudinal direction L until the cap 22contacts the spinal rod 14.

The cap 22 can include a single piece, or as shown in the illustratedembodiment, a multiple piece, for example two-pieces. The cap 22includes threads 38, for example external threads, that are configuredto threadingly engage with threads 40, for example internal threads, ofthe anchor body 16. The cap 22 is rotated in a first direction ofrotation about an axis, for example an axis parallel to the longitudinaldirection L, such that the threads 38 engage with the threads 40 and thecap 22 moves in the longitudinal direction L with respect to the anchorbody 16. According to one embodiment, the cap 22 is configured to berotated until the cap 22 is no longer rotatable in the first directionof rotation when a set torque is applied to the cap 22, thereby securingthe spinal rod 14 to the fastener device 12 such that relative movementof the spinal rod 14 and the fastener device 12 is limited, for exampleprevented, and thereby securing the fastener 18 to the anchor body 16such that relative movement of the fastener 18 and the anchor body 16 islimited, for example prevented. According to one embodiment, the settorque is between about 2 Newton-meters (N-m) and about 3 N-m.

Referring to FIGS. 3 to 5 , the head 32 of the fastener 18 includes anouter surface 42. According to one aspect of the disclosure, a portion44 of the outer surface 42 may be convex, may define a portion of afirst sphere S1, or both. The first sphere S1 defines a first diameterD1. According to one aspect of the disclosure, the first diameter D1 maybe greater than about 4.5 mm. According to another aspect of thedisclosure, the first diameter D1 may be greater than about 5.0 mm.According to another aspect of the disclosure, the first diameter D1 maybe in a range between about 5.0 mm and about 8.0 mm. According toanother aspect of the disclosure, the first diameter D1 may be about 6.0mm.

The outer surface 42 may include one or more additional portions that donot define a portion of the first sphere S1. As shown in the illustratedembodiment, the outer surface 42 may include a distal portion 46 that ispositioned in the distal direction D with respect to the portion 44, aproximal portion 48 that is positioned in a proximal direction P, whichis opposite the distal direction D, with respect to the portion 44, orboth the distal portion 46 and the proximal portion 48. According toanother aspect of the disclosure, an entirety of the outer surface 42may include the portion 44, such that the outer surface 42 is devoid ofthe distal portion 46 and the proximal portion 48.

The head 32 of the fastener 18 may define a location 50 such that thefastener 18 is devoid of any locations positioned in the proximaldirection P from the location 50. As shown in the illustratedembodiment, the head 32 includes an upper surface 52 that defines adrive mechanism 54, the drive mechanism 54 configured to receive adriving force that rotates the fastener 18 to secure the fastener 18 toa vertebra. According to one aspect of the disclosure, the upper surface52 can be substantially flat, such that any point on the upper surface52 can define the location 50. According to another aspect of thedisclosure, the upper surface 52 can be not flat, for example curvedsuch that an apex of the upper surface 52 defines the location 50.

According to one aspect of the disclosure, the fastener 18 may include asurface 56 that extends along both the head 32 and the neck 36. As shownin the illustrated embodiment, the surface 56 may be concave such thatthe surface 56 defines a radius of curvature R. According to oneembodiment, the radius of curvature R may be constant along an entiretyof the surface 56. For example, the surface 56 may define a radius ofcurvature R of between about 0.25 mm and about 2.0 mm. According toanother example, the surface 56 may define a radius of curvature R ofbetween about 0.4 mm and about 1.0 mm. According to another embodiment,the radius of curvature R may vary along the surface 56. According toanother embodiment, the surface 56 may include two perpendicularsurfaces such that the surface 56 does not define a radius of curvatureR.

The portion of the fastener 18 between the head 32 and the shaft 34, forexample the neck 36, is a potential area where the fastener 18 may failunder load. According to one aspect of the disclosure, radius ofcurvature R of the concave surface 56, may distribute stresses withinthe fastener 18, thereby increasing the effective strength of thefastener 18. For example, a first fastener 18 that defines a firstradius of curvature R that is larger than a second radius of curvaturedefined by a second fastener 18 may result in a better distribution ofstresses under load in the first fastener 18 when compared to the secondfastener 18, and thus the first fastener 18 may have an increasedeffective strength compared to the second fastener 18.

According to one aspect of the disclosure, the neck 36 defines a seconddiameter D2 that may be measured both in a direction perpendicular tothe distal direction D and at a location 57 that is in the distaldirection D with respect to the surface 56. As shown in the illustratedembodiment, the second diameter D2 may be measured both in the distaldirection D and at the location 57 which is in the distal direction Dwith respect to an entirety of the surface 56 which defines the radiusof curvature R. The second diameter D2 may be constant such that thesecond diameter D2 at first and second locations spaced apart withrespect to the distal direction D, is the same. Alternatively, thesecond diameter D2 may vary, for example decrease in the distaldirection D2.

According to another aspect of the disclosure, the second diameter D2may be in a range between about 1.0 mm and about 4.0 mm. According toanother aspect of the disclosure, the second diameter D2 may be about2.5 mm. The fastener 18 defines a ratio of the first diameter D1 to thesecond diameter D2. According to one aspect of the disclosure, the ratioof the first diameter D1 to the second diameter D2 is in a range betweenabout 2 to 1 and about 3 to 1.

The fastener 18 may be elongate along an axis, for example a centralfastener axis 58. As shown in the illustrated embodiment, the centralfastener axis 58 is parallel to the distal direction D. According to oneaspect of the disclosure, the portion 44 of the outer surface 42 mayinclude a first point 60 that is located in the distal direction withrespect to all other points of the portion 44 of the outer surface 42,the surface 56 includes a second point 62 that is located in theproximal direction P with respect to all other points of the surface 56,the first point 60 is spaced from the central fastener axis 58 a firstdistance L1 measured in a direction perpendicular to the distaldirection D, the second point 62 is spaced from the central fasteneraxis 58 a second distance L2 measured in a direction perpendicular tothe distal direction D, and the first distance L1 is greater than thesecond distance L2.

The head 32 may include an intermediate surface 64 that extends betweenthe surface 56 and the outer surface 42. According to one aspect of thedisclosure, at least a portion of the intermediate surface 64 may besubstantially flat and perpendicular to the distal direction D.

The fastener 18 may be configured such that all lines that both lieentirely within a plane P1 that is parallel to the distal direction Dand that are tangent to the portion 44 of the outer surface 42 arenoncollinear with all lines that both lie entirely within the plane P1and that are tangent to the surface 56. For example, a line 66 whichboth lies entirely within the plane P1 and is tangent to the portion 44is not collinear with a line 68 which both lies entirely within theplane P1 and is tangent to the surface 56.

Referring to FIGS. 6 and 7 , the anchor body 16 may define arod-receiving channel 69 that is configured to receive a spinal rod, forexample the spinal rod 14 (as shown in FIG. 1 ). The rod-receivingchannel 69 extends through the anchor body housing 28 and may beoriented such that the rod-receiving channel 69 is offset from, forexample perpendicular to, the through hole 30. As shown in theillustrated embodiment, the rod-receiving channel 69 may be a U-shapedchannel.

The anchor body 16 may further include an inner surface 70 that definesat least a portion of the through hole 30. According to one aspect ofthe disclosure, a portion 72 of the inner surface 70 may be concave, maydefine a portion of a second sphere S2, or both. The second sphere S2defines a third diameter D3. According to one aspect of the disclosure,the third diameter D3 is equal to the first diameter D1. According toanother aspect of the disclosure, the third diameter D3 is eithergreater than or less than the first diameter D1.

The inner surface 70 defines a minimum inner diameter D4 that ismeasured both in a direction perpendicular to the longitudinal directionL and at a location 74 that is closer to the lower end 26 as measuredalong the longitudinal direction L than the location 74 is to the upperend 24 as measured along the longitudinal direction L. As shown in theillustrated embodiment, the location 74 may be spaced a distance fromthe lower end 26 measured along the longitudinal direction L, such thatthe inner surface 70 tapers radially outward with respect to a centralanchor body axis 76 as the inner surface 70 extends from the location 74to the lower end 26. According to another aspect of the disclosure, thelocation 74 may be located at the lower end 26. According to oneembodiment, the location 74 may be positioned on the portion 72 suchthat no point on the portion 72 is positioned in the longitudinaldirection L with respect to the location 74.

The anchor body 16 defines an inner diameter D5 that is greater than theminimum inner diameter D4. According to one aspect of the disclosure,the inner diameter D5 may be defined by the inner surface 70 at alocation that is spaced from the portion 72 in a direction opposite thelongitudinal direction L. According to another aspect of the disclosure,the inner diameter D5 may be defined by the upper end 24. According toone aspect of the disclosure, the inner diameter D5 may be a maximuminner diameter of the anchor body 16.

According to one aspect of the disclosure, the upper end 24 defines anupper opening 78 where the through hole 30 exits the anchor body housing28 in the direction opposite the longitudinal direction L, the lower end26 defines a lower opening 80 where the through hole 30 exits the anchorbody housing 28 in the longitudinal direction L, or both. As shown inthe illustrated embodiment, the anchor body 16 may define a plane P2(shown as a line which extends into and out of the page). The plane P2may include an entirety of the lower opening 80, may be perpendicular tothe longitudinal direction L, or both.

Referring to FIGS. 8 and 9 , the fastener device 12 defines an assembledconfiguration in which the portion 44 of the outer surface 42 ridesalong (contacts at more than one point) the portion 72 of the innersurface 70 such that the fastener 18 is movable with respect to theanchor body 16. The contact between the portion 44 and the portion 72may define a circle, a portion of a circle, a portion of a sphere, orany combination thereof. According to one aspect of the disclosure, thefastener 18 is movable polyaxially with respect to the anchor body 16such that the fastener device 12 defines a cone of angulation thatincludes all of the angles at which the central fastener axis 58 and thecentral anchor body axis 76 can be offset from one another when thefastener device 12 is in the assembled configuration. The cone ofangulation may be defined by a maximum angle α (alpha), for example thecone of angulation may be twice the maximum angle α (alpha).

The maximum angle α (alpha) is measured between the central fasteneraxis 58 and the central anchor body axis 76 when the anchor body 16abuts the neck 36 at a location that is spaced in the distal direction Dfrom an entirety of the surface 56 such that movement of the fastener 18relative to the anchor body 16 in at least one direction is blocked.According to one aspect of the disclosure the maximum angle α (alpha) isgreater than about 45 degrees. According to another aspect of thedisclosure the maximum angle α (alpha) is greater than about 50 degrees.According to another aspect of the disclosure the maximum angle α(alpha) is between about 50 degrees and about 60 degrees. For example,the fastener device 12 may be configured as a cervical fastener devicewith a maximum angle α (alpha) of about 50 degrees. As another examplethe fastener device 12 may be configured as a lumbar fastener devicewith a maximum angle α (alpha) of about 30 degrees.

As shown in FIG. 8 , when the fastener device 12 is in the configurationthe central fastener axis 58 and the central anchor body axis 76 may beparallel, for example collinear. As shown in FIG. 9 , when the fastenerdevice 12 is in the configuration the central fastener axis 58 and thecentral anchor body axis 76 may be angularly offset, for example by themaximum angle α (alpha) or by any angle less than maximum angle α(alpha).

Referring to FIGS. 5, 7, and 8 , because the first diameter D1 is largerthan the minimum inner diameter D4 the head 32 of the fastener 18 is notable to be inserted into the through hole 30 along the directionopposite the longitudinal direction L such that the portion 44 of theouter surface 42 rides along the portion 72 of the inner surface 70.Instead, because the inner diameter D5 is greater than the firstdiameter D1, the fastener 18 is configured to be inserted into thethrough hole 30 along the longitudinal direction L such that the portion44 of the outer surface 42 rides along the portion 72 of the innersurface 70. Thus the fastener device 12 can be described as atop-loading fastener device as opposed to a bottom-loading (or pop-on)fastener device. The fastener device 12 being configured as atop-loading fastener device allows the size of the first diameter D1 andthe size of the second diameter D2 to remain larger than in a comparablebottom-loading screw, which can result in a fastener device 12, andspecifically a fastener 18, with increased strength.

Referring to FIG. 9 , according to one aspect of the disclosure thefastener device 12 defines a configuration in which the location 50 ispositioned a third distance L3 from the upper end 24 measured along thelongitudinal direction L, the lower end 26 is positioned a fourthdistance L4 from the upper end 24 measured along the longitudinaldirection L, and the third distance L3 is greater than the fourthdistance L4. According to one aspect of the disclosure the fastenerdevice 12 defines a configuration in which the location 50 is spaced inthe longitudinal direction L with respect to the plane P2.

According to one aspect of the disclosure, the fastener device 12defines a configuration (referred to herein as a maximum angledconfiguration) in which both the portion 44 of the outer surface 42rides along the portion 72 of the inner surface 70, and the anchor body16 abuts the neck 36 at the location 57 that is spaced in the distaldirection D from an entirety of the surface 56 such that movement of thefastener 18 relative to the anchor body 16 in at least one direction isblocked.

Referring to FIGS. 8 and 9 , the fastener device 12 is illustrated withthe saddle 20 abutting the fastener 18, and the spinal rod 14 and thecap 22 are not shown. The description of FIGS. 8 and 9 applies to thefastener device 12 with and without any combination of the saddle 20,the cap 22, and the spinal rod 14.

As shown in the illustrated embodiment, when the fastener device 12 isin the maximum angled configuration a gap 84 is defined between thesurface 56 and the anchor body 16. The gap 84 is enclosed in both thelongitudinal direction L and the direction opposite the longitudinaldirection L. According to one aspect of the disclosure, when thefastener device is in the maximum angled configuration, a region ofcontact that includes all of the points of contact between the anchorbody 16 and the fastener 18 as measured in a plane that is perpendicularto the longitudinal direction L defines a portion of a circle that isless than a full circle.

Referring to FIGS. 4 and 9 , according to one aspect of the disclosurethe strength of the fastener 18 may be increased by maximizing thesecond diameter D2. However, increasing the size of the second diameterD2 while not changing other dimensions of the fastener 18, for examplethe first diameter D1, may result in a fastener device 12 with a lowermaximum angle α (alpha). Accordingly, maximizing the second diameter D2while maintaining the ratio of the first diameter D1 to the seconddiameter D2 may result in a fastener 18 with increased strength and afastener device 12 with a greater maximum angle α (alpha). According toone aspect of the disclosure the strength of the fastener 18 may beincreased by increasing the size of the radius of curvature R. Theincreased size of the radius of curvature R may result in less materialbeing present in the area between the head 32 and the threaded shaft 34,however the large radius of curvature may reduce stress concentrationswithin the area between the head 32 and the threaded shaft 34, therebyresulting in increased strength of the fastener 18.

Additionally, in the fastener device 12 as shown in the illustratedembodiment the portion 44 of the outer surface 42 articulates along orrides along the portion 72 of the inner surface 70 such that the portion44 directly contacts the portion 72. According to the illustratedembodiment, the fastener device may be devoid of a collet or otherintermediate structure between the portion 44 and the portion 72. Theinclusion of a collet or other intermediate structure positioned withinthe through hole 30 of a given size would result in the use of afastener with a first diameter D1 being smaller than the first diameterD1 of the fastener 18 which is configured for use with the fastenerdevice 12 that is devoid of a collet or other intermediate structure.Thus, the fastener device 12 being devoid of a collet or otherintermediate structure between the portion 44 and the portion 72 mayresult in increased strength in the fastener 18 configured for use withthe fastener device 12.

Referring to FIGS. 1 to 9 , a method of making the fastener device 12may include the step of inserting the fastener 18 into the anchor body16 such that the threaded shaft 34 passes through the lower opening 80of the anchor body 16. The method of making the fastener device 12 mayfurther include the steps of: inserting the saddle 20 into the anchorbody 16; inserting the spinal rod 14 into the anchor body 16; insertingthe cap 22 into the anchor body 16; or any combination thereof.

The method of making the fastener device 12 may further include the stepof tightening the cap 22. According to one aspect of the disclosure, thefastener device 12 is configured such that after the step of insertingthe fastener 18 into the anchor body 16, and before the tightening stepthe fastener 18 is freely movable within the through hole 30 withrespect to the anchor body 16, and vice versa. The fastener 18 beingfreely movable includes the fastener 18 being translatable with respectto the anchor body 16 along the longitudinal direction L, the fastener18 being polyaxially rotatable with respect to the anchor body 16, orboth.

Referring to FIGS. 10 and 11 , the fastener 18 being freely movablewithin the through hole 30 with respect to the anchor body 16 may resultin undesired movement of the anchor body 16 relative to the fastener 18during insertion of the fastener 18 into hole 30. As shown in theillustrated embodiment of FIG. 10 , during insertion, the fastener 18and the anchor body 16 may be offset with respect to the longitudinaldirection L, for example the central fastener axis 58 and the centralanchor body axis 76 may be angularly offset by an angle, β (beta). Theangular offset of the central fastener axis 58 and the central anchorbody axis 76 may result in a force, such as the force of gravity on theanchor body 16, being sufficient to move the anchor body 16 relative tothe fastener 18, for example until the neck 36 of the fastener 18contacts the anchor body 16, as shown in FIG. 11 .

Referring to FIGS. 12 to 17 , the fastener device 12 may include abiasing member 102 configured to restrict, for example by providing aforce, relative movement of the anchor body 16 and the fastener 18 afterthe fastener 18 is inserted into the anchor body 16, and before the cap22 is inserted into the through hole 30 such that the cap 22 abuts thespinal rod 14.

Biasing member 102 may be disposed in a recess 106 in anchor body 16such that movement of the biasing member 102 relative to the anchor body16 is limited in a direction, for example a direction parallel to thecentral anchor body axis 76. The biasing member 102 may further beconfigured to provide a force on the outer surface 42 of the fastener18. As shown in the illustrated embodiment, the biasing member 102 maybe a split ring. According to another embodiment, the biasing member 102may be a non-circular shape, such as but not limited to a polygonalshape. As shown in the illustrated embodiment, the recess 106 may bedefined by the anchor body 16.

According to one aspect of the disclosure, the biasing member 102 may beconfigured to expand radially with respect to the central anchor bodyaxis 76. For example, before the fastener 18 is inserted into thethrough hole 30, the biasing member 102 defines an inner diameter D6having a first dimension. The biasing member 102 may be configured toexpand as the fastener 18 is inserted into the through hole 30, and theouter surface 42 of the fastener contacts the biasing member 102. Oncethe fastener 18 is fully seated within the through hole 30, such that nofurther movement of the fastener 18 in the longitudinal direction Lrelative to the anchor body 18, is possible due to the outer surface 42abutting the inner surface 70, the inner diameter D6 has a seconddimension that is larger than the first dimension. The biasing member102 is configured such that increasing the size of the inner diameter D6imparts a force on the outer surface 44 of the fastener 18. According toone aspect of the disclosure, the fastener device 12 is configured suchthat the biasing member 102 imparts the force on the outer surface 42 ina direction substantially perpendicular to the central anchor body axis76.

Referring to FIG. 13 , the biasing member 102 includes an inner surface112 and an outer surface 114. As shown in the illustrated embodiment,the inner surface 112 defines a through hole 115 that extends throughthe biasing member 100. The inner surface 112 may define at least aportion, for example greater than half of, a circle. The circle of whichat least a portion is defined by the inner surface 112 may include acenter 116. The inner diameter D6 is measured along a straight line froma first point on the inner surface 112, through the center 116, to asecond point on the inner surface 112 spaced apart from the first point.

The biasing member 102 may further define an outer diameter D7 measuredalong a straight line from a first point on the outer surface 114,through the center 116, to a second point on the outer surface 114spaced apart from the first point on the outer surface 114. The outerdiameter D7 is greater than the inner diameter D6.

Referring to FIG. 14 , the inner surface 70 of the anchor body 16defines the recess 106. The recess 106 extends radially into the innersurface 70 of the anchor body 16 and terminates at a base surface 118.The recess 106 further extends into the inner surface 70 of the anchorbody 16 such that the recess 106 defines a recess height RH. The recessheight RH is measured along a straight line that is parallel to thecentral anchor body axis 76 from a recess upper surface 120 to a recesslower surface 122. The anchor body 16 defines an inner diameter D8measured along a straight line that is perpendicular to the centralanchor body axis 76 from a first point on the base surface 118, throughthe central anchor body axis 76, to a second point on the base surface118 that is spaced from the first point.

The anchor body 16 further defines an inner diameter D9 measured along astraight line that is perpendicular to the central anchor body axis 76from a first point on the inner surface 70 that is offset from therecess in the direction opposite the longitudinal direction L, throughthe central anchor body axis 76, to a second point on the inner surface70 that is spaced from the first point. The anchor body 16 furtherdefines an inner diameter D10 measured along a straight line that isperpendicular to the central anchor body axis 76 from a first point on aportion 86 of the inner surface 70 that is offset from the recess in thelongitudinal direction L, through the central anchor body axis 76, to asecond point on the portion 86 of the inner surface 70 that is spacedfrom the first point. According to one aspect of the disclosure, theinner diameter D8 is larger than both the inner diameter D9 and theinner diameter D10. As shown in the illustrated embodiment, the portion86 may be curved and define a portion of a sphere having a diameter.

Referring to FIGS. 12 to 15 , the biasing member 102 includes anunbiased state when the fastener 18 is not abutting the inner surface112 and the anchor body 16 is not abutting the outer surface 114. Thebiasing member 102 further includes a biased state when the fastener 18is abutting the inner surface 112, the anchor body 16 is abutting theouter surface 114, or both. The fastener device 12 may be configuredsuch that the biasing member 102 is configured to be positioned withinthe recess 106. According to one aspect of the disclosure, the biasingmember 102 is configured to be in the unbiased state when positionedwithin the recess 106, and the recess 106 is configured to retain thebiasing member 102 within the recess 106, as shown in FIG. 15 .

As shown in the illustrated embodiment, the fastener device 12 may beconfigured such that, in the unbiased state, the inner diameter D6 issmaller than both the inner diameter D9 and the inner diameter D10, theouter diameter D7 is larger than both the inner diameter D9 and theinner diameter D10, and the inner diameter D8 is larger than the outerdiameter D7. The biasing member 102, in the unbiased state, is disposedwithin the recess 106 such that movement of the biasing member 102 outof the recess along the longitudinal direction L is blocked by the uppersurface 120 and the lower surface 122. The recess 106 further providesroom for the biasing member 102 to expand radially out toward the basesurface 118.

The biasing member 102 may further include a top surface 130 and abottom surface 132 opposite the top surface 130. As shown in theillustrated embodiment, the bottom surface 132 faces in the longitudinaldirection L and the top surface 130 faces in the direction opposite thelongitudinal direction L. The biasing member 102 may further include oneor more tapered surfaces 134. The one or more tapered surfaces 134 mayinclude a first tapered surface 134′ that extends between the uppersurface 130 and the inner surface 112, a second tapered surface 134″that extends between the lower surface 132 and the inner surface 112, orboth. The one or more tapered surfaces 134 may be linear, curved, orpartially linear and partially curved. The one or more tapered surfaces134 are configured to enable easier entry of the fastener 18 into thethrough hole 115, for example by lowering the amount of force requiredcompared to a biasing member 102 devoid of the one or more taperedsurfaces 134.

Referring to FIG. 16 , the fastener 18 is configured to be inserted intothe through hole 30 such that the threaded shaft 34 extends through thelower opening 80 and the outer surface 42 abuts the inner surface 112,thereby transitioning the biasing member 102 into a biased state. Thefastener device 12 may define a fully seated configuration in which theouter surface 42 abuts the portion 86 of the inner surface 70. When thefastener device 12 is in the fully seated configuration the biasingmember 102 exerts a force on the fastener 18, and that force resistsrelative to movement of the fastener 18 and the anchor body 16.

Relative movement of the fastener 18 and the anchor body 16 along thelongitudinal direction L is resisted by the biasing member 102, which isexerting an inward radial force on the fastener 18, abutting either theupper surface 120 or the lower surface 122. Relative rotation, forexample polyaxial rotation, of the fastener 18 and the anchor body 16 isresisted by a drag force or friction force resulting from the inwardradial force exerted by the biasing member 102 on the fastener 18.

According to one aspect of the disclosure, the fastener 18 defines awidest location 136 that is larger, as measured along a straight lineperpendicular to the central fastener axis 58 from a first point on theouter surface 42, through the central fastener axis 58, to a secondpoint on the outer surface 42, than any other location on the head 32.The fastener device 12 may be configured such that in the fully seatedconfiguration, when the central fastener axis 58 is parallel to thecentral anchor body axis 76, the biasing member 102 abuts the outersurface 42 at a location aligned with the widest location 136 withrespect to the distal direction D.

According to another embodiment, the fastener device 12 may beconfigured such that in the fully seated configuration, when the centralfastener axis 58 is parallel to the central anchor body axis 76, thebiasing member 102 abuts the outer surface 42 at a location eitherspaced from the widest location 136 in the distal direction D, or spacedfrom the widest location 136 in the proximal direction P.

The method of making the fastener device 12 may include the step ofinserting the fastener 18 into the biasing member 102 until the outersurface 42 abuts the portion 86 of the inner surface 70. The above stepof inserting the fastener 18 into the biasing member 102 may include thestep of radially expanding the biasing member 102 such that the innerdiameter D6 increases. The above step of inserting the fastener 18 intothe biasing member 102 may further include, after the step of radiallyexpanding the biasing member 102, the step of radially contracting thebiasing member 102 such that the inner diameter D6 decreases.

Referring to FIG. 17 , the biasing member 102 is configured to resistundesired relative movement of the fastener 18 and the anchor body 16,but allow desired relative movement of the fastener 18 and the anchorbody 16. In use, when the fastener 18 is in the fully seatedconfiguration, the anchor body 16 may be moved relative to the fastener18, for example by a surgeon manipulating at least one of the fastener18 and the anchor body 16. Additionally, when the fastener 18 is in thefully seated configuration, the biasing member 102 prevents relativemovement of the anchor body 16 relative to the fastener 18, for exampledue to gravity acting on the anchor body 16 when the central fasteneraxis 58 is angular offset from the central anchor body axis 76 by theangle β (beta). According to one aspect of the disclosure, the angle β(beta) may be between 0 and the maximum angle α (alpha).

The description of the biasing member 102 illustrated in FIGS. 12 to 17also applies to the embodiments illustrated in FIGS. 1 to 11 .Additionally, the description of the embodiments illustrated in FIGS. 1to 11 is applicable to the embodiments illustrated in FIGS. 12 to 17 .

It will be appreciated that the foregoing description provides examplesof the disclosed system and technique. However, it is contemplated thatother implementations of the disclosure may differ in detail from theforegoing examples. All references to the disclosure or examples thereofare intended to reference the particular example being discussed at thatpoint and are not intended to imply any limitation as to the scope ofthe disclosure more generally. All language of distinction anddisparagement with respect to certain features is intended to indicate alack of preference for those features, but not to exclude such from thescope of the disclosure entirely unless otherwise indicated.

Recitation of ranges of values herein are merely intended to serve as ashorthand method of referring individually to each separate valuefalling within the range including the stated ends of the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context.

Although the disclosure has been described in detail, it should beunderstood that various changes, substitutions, and alterations can bemade herein without departing from the spirit and scope of the inventionas defined by the appended claims. Moreover, the scope of the presentdisclosure is not intended to be limited to the particular embodimentsdescribed in the specification. As one of ordinary skill in the art willreadily appreciate from the disclosure of the present invention,processes, machines, manufacture, composition of matter, means, methods,or steps, presently existing or later to be developed that performsubstantially the same function or achieve substantially the same resultas the corresponding embodiments described herein may be utilizedaccording to the present disclosure.

We claim:
 1. A fastener device configured to secure a spinal rodrelative to a bone, the fastener device comprising: an anchor bodyincluding an anchor body housing, the anchor body defining a throughhole that extends through the anchor body housing, the anchor bodyfurther defining a rod-receiving channel that is configured to receivethe spinal rod, the anchor body further including an upper end, a lowerend, and an inner surface, the inner surface defining at least a portionof the through hole; and a fastener including a head, a threaded shaftthat extends out with respect to the head in a distal direction, and aneck that extends between the head and the threaded shaft, the headincluding a convex outer surface, a portion of the convex outer surfaceboth defining a portion of a sphere and being configured to articulaterelative to the inner surface when the head is positioned in the throughhole, the fastener including a concave surface that extends along both adistal most portion of the head and the neck, wherein the fastener isconfigured such that all lines that: 1) lie entirely within a planeparallel to the distal direction, and 2) are tangent to the portion ofthe convex outer surface are noncollinear with all lines that: 1) lieentirely within the plane, and 2) are tangent to the concave surface. 2.The fastener device of claim 1, wherein the through hole extends awayfrom the upper end and toward the lower end in a longitudinal direction,and the inner surface defines a minimum inner diameter at an anchorlocation on the inner surface, such that the anchor location is closerto the lower end as measured along the longitudinal direction, than theanchor location is to the upper end as measured along the longitudinaldirection.
 3. The fastener device of claim 1, wherein the lower enddefines a lower opening where the through hole exits the anchor bodyhousing, the anchor body defines a plane that includes an entirety ofthe lower opening, the head of the fastener defines a fastener locationsuch that the fastener is devoid of any locations positioned in aproximal direction, which is opposite the distal direction, from thefastener location, and the fastener device defines a configuration inwhich the fastener location is positioned a first distance from theupper end, the lower end is positioned a second distance from the upperend, the first distance and the second distance are each measured alongthe longitudinal direction, and the first distance is greater than thesecond distance.
 4. The fastener device of claim 1, wherein the spheredefines a first diameter, the through hole extends along a centralanchor body axis, the inner surface defines a minimum inner diameterthat is both: 1) measured at a location that is on the inner surface,and 2) measured in a direction perpendicular to the central anchor bodyaxis, and the first diameter is larger than the minimum inner diameter.5. The fastener device of claim 1, further comprising a stabilizationmechanism configured to be positioned in the through hole such that whenthe fastener is inserted in the through hole such that the outer surfacecontacts the inner surface the stabilization mechanism exerts a force onthe fastener that resists relative movement of the fastener and theanchor body.
 6. The fastener device of claim 5, wherein thestabilization mechanism includes a biasing member configured to expandas the head of the fastener contacts the biasing member, such that theexpanded biasing member exerts the force on the outer surface of thefastener.
 7. The fastener device of claim 6, wherein the anchor bodydefines a recess configured to receive the biasing member such that thebiasing member is captured within the recess.
 8. The fastener device ofclaim 1, wherein the portion of the sphere terminates at an intermediatesurface that terminates at the concave surface, and wherein theintermediate surface is flat or has a curvature different from theportion of the sphere and the concave surface.
 9. The fastener device ofclaim 1, wherein the portion of the convex outer surface defines everylocation on the head that is configured to contact the inner surfacewhen the head is positioned in the through hole, wherein the portion ofthe sphere terminates at an intermediate surface that terminates at theconcave surface, and wherein the intermediate surface is flat or has acurvature different from the portion of the sphere and the concavesurface.
 10. A fastener device configured to secure a spinal rodrelative to a bone, the fastener device comprising: an anchor bodyincluding an anchor body housing and a central axis, the anchor bodydefining a through hole that extends through the anchor body housingalong the central axis, the anchor body further defining a rod-receivingchannel that is configured to receive the spinal rod, the anchor bodyfurther including an upper end, a lower end spaced from the upper end ina first direction, and an inner surface that defines at least a portionof the through hole, the inner surface including: 1) a first portionthat defines a portion of a sphere having a first diameter, 2) a secondportion that is cylindrical and that defines a second diameter that isequal to or greater than the first diameter, and 3) a third portion thatdefines a recess that defines a third diameter that is greater than boththe first diameter and the second diameter, wherein the portion of thesphere terminates at a first end of the recess in a direction that isopposite the first direction, and the third portion is disposed betweenthe first portion and the second portion with respect to the firstdirection; and a fastener including a head and a threaded shaft thatextends out with respect to the head, the head including an outersurface configured to articulate relative to the first portion of theinner surface when the head is inserted in the through hole.
 11. Thefastener device of claim 10, further comprising a biasing memberconfigured to be inserted into the through hole and positioned such thatthe biasing member is aligned with the third portion along a seconddirection that is perpendicular to the first direction.
 12. The fastenerdevice of claim 11, wherein the biasing member is a split ring thatincludes an inner surface that faces the central axis when the splitring is inserted in the through hole, the split ring defines a fourthdiameter measured from a first point on the inner surface, through thecentral axis, to a second point on the inner surface in the seconddirection, and when the split ring is in an unbiased state the fourthdiameter is less than each of the first diameter, the second diameter,and the third diameter.
 13. The fastener device of claim 10, wherein thesphere is a first sphere, the threaded shaft extends out with respect tothe head in a distal direction, the fastener includes a neck thatextends between the head and the threaded shaft, at least a portion ofthe outer surface is convex and defines a portion of a second sphere,the second sphere defining a first fastener diameter, the fastenerincludes a concave surface that extends along both the head and theneck, the neck defines a second fastener diameter measured: 1) in adirection perpendicular to the distal direction, and 2) at a locationspaced in the distal direction of an entirety of the concave surface,and the fastener defines a ratio of the first fastener diameter to thesecond fastener diameter in a range between about 2 to 1 and about 3to
 1. 14. The fastener device of claim 13, wherein: the fastener iselongate along a central axis that is parallel to the distal direction;the portion of the outer surface includes a first point that is locatedin the distal direction with respect to all other points of the portionof the outer surface; the concave surface includes a second point thatis located in a proximal direction which is opposite the distaldirection, with respect to all other points of the concave surface; andthe first point is spaced from the central axis a first distancemeasured in a direction perpendicular to the distal direction, thesecond point is spaced from the central axis a second distance measuredin a direction perpendicular to the distal direction, and the firstdistance is greater than the second distance.
 15. The fastener device ofclaim 14, wherein the location is a first location, the through holeextends away from the upper end and toward the lower end in alongitudinal direction, and the inner surface defines a minimum innerdiameter that is both: 1) measured at a second location that is on theinner surface, and 2) measured in a direction perpendicular to thelongitudinal direction, the second location is closer to the lower endas measured along the longitudinal direction, than the second locationis to the upper end as measured along the longitudinal direction. 16.The fastener device of claim 10, wherein the recess faces toward thehead of the fastener when the fastener is in a first configuration inwhich the outer surface is in contact with the portion of the sphere.17. A fastener device configured to secure a spinal rod relative to abone, the fastener device comprising: an anchor body including an anchorbody housing and a central axis, the anchor body defining a through holethat extends through the anchor body housing along the central axis, theanchor body further defining a rod-receiving channel that is configuredto receive the spinal rod, the anchor body further including an upperend, a lower end spaced from the upper end in a first direction, and aninner surface that defines at least a portion of the through hole, theinner surface including: 1) a first portion that defines a portion of asphere having a first diameter, 2) a second portion that is cylindricaland that defines a second diameter that is equal to or greater than thefirst diameter, and 3) a third portion that defines a third diameterthat is greater than both the first diameter and the second diameter,wherein the first portion terminates at the third portion in a directionthat is opposite the first direction, and the third portion is disposedbetween the first portion and the second portion with respect to thefirst direction; a fastener including a head and a threaded shaft thatextends out with respect to the head, the head including an outersurface configured to articulate along the first portion of the innersurface when the head is inserted in the through hole; and a biasingmember configured to be inserted into the through hole and positionedsuch that the biasing member is aligned with the third portion along asecond direction that is perpendicular to the first direction, whereinthe biasing member is a split ring that includes an inner surface thatfaces the central axis when the split ring is inserted in the throughhole, the split ring defines a fourth diameter measured from a firstpoint on the inner surface, through the central axis, to a second pointon the inner surface in the second direction, and when the split ring isin an unbiased state the fourth diameter is less than each of the firstdiameter, the second diameter, and the third diameter.
 18. The fastenerdevice of claim 17, wherein the split ring includes an outer surfacethat faces away from the central axis when the split ring is inserted inthe through hole, the split ring defines a fifth diameter measured froma first point on the outer surface, through the central axis, to asecond point on the outer surface in the second direction, and when thesplit ring is in an unbiased state the fifth diameter is: 1) greaterthan the first diameter, 2) greater than the second diameter, 3) andless than the third diameter.
 19. The fastener device of claim 17,wherein the sphere is a first sphere, the threaded shaft extends outwith respect to the head in a distal direction, the fastener includes aneck that extends between the head and the threaded shaft, at least aportion of the outer surface is convex and defines a portion of a secondsphere, the second sphere defining a first fastener diameter, thefastener includes a concave surface that extends along both the head andthe neck, the neck defines a second fastener diameter measured: 1) in adirection perpendicular to the distal direction, and 2) at a locationspaced in the distal direction of an entirety of the concave surface,and the fastener defines a ratio of the first fastener diameter to thesecond fastener diameter in a range between about 2 to 1 and about 3to
 1. 20. The fastener device of claim 19, wherein: the fastener iselongate along a central axis that is parallel to the distal direction;the portion of the outer surface includes a first point that is locatedin the distal direction with respect to all other points of the portionof the outer surface; the concave surface includes a second point thatis located in a proximal direction which is opposite the distaldirection, with respect to all other points of the concave surface; andthe first point is spaced from the central axis a first distancemeasured in a direction perpendicular to the distal direction, thesecond point is spaced from the central axis a second distance measuredin a direction perpendicular to the distal direction, and the firstdistance is greater than the second distance.